The present invention relates to carbonless copying systems, and more specifically, a carbonless copying system which enables the formation on a substrate, e.g., on a sheet of paper, of images having three or more different colors.
As described in U.S. Pat. No. 4,636,818, standard carbonless copying systems include a plurality of substrates, e.g., paper sheets, arranged in a manifold, each sheet having one or more coatings on its surface. The manifold is designed so that when external pressure caused by a typewriter, pen, or other instrument is applied to the outermost sheet, a colored image will be formed on at least one surface of each sheet of the manifold.
The top sheet of the manifold to which the pressure is applied has a coating on its back surface. This coated back surface includes microcapsules containing an initially colorless chemically reactive color-forming dye precursor as the fill material. The front surface of the next sheet, which is adjacent to the back surface of the top sheet, is coated with a material containing a component, such as phenolic resin or reactive clay, that is capable of reacting with the colorless dye precursor contained in the microcapsules to produce a color. Thus, an external pressure on the front surface of the top sheet will rupture the microcapsules on the back surface and release the colorless dye precursor which then chemically reacts with the reactive component of the coated front of the adjacent sheet to produce a colored image corresponding to the area of pressure. Similarly, colored images are produced on each successive sheet of the manifold by the external pressure rupturing the microcapsules carried on the bottom surface of each sheet.
The sheets of the carbonless copying system manifold are designated in the art by the terms CB for "coated back", CFB for "coated front and back", and CF for "coated front". The CB or transfer sheet is usually the top sheet of the manifold and the sheet to which the external pressure is applied. The CFB sheets are the intermediate sheets of the manifold, each of which is able to have an image formed on its front surface by a pressure, and each of which also transmits the contents of ruptured microcapsules from its back surface to the front surface of the next sheet. The CF or recording sheet is the bottom sheet and is coated only on its front surface so that an image can be formed on it.
While it is customary to have the coating containing the microcapsules on the back surface of the sheets and to have the coating containing the reactive component for the capsules on the front surface of each of the sheets, the reverse arrangement is also possible. In addition, one of the reactive ingredients may be carried in the sheets themselves, rather than applied as surface coatings. Furthermore, the component that reacts with the colorless dye precursor may also be microencapsulated.
The microcapsules used in carbonless copying systems generally comprise a core of fill material surrounded by a wall or shell of polymeric material. The wall surrounding the fill material acts to isolate the fill material from the external environment. To release the fill material, e.g., the dye precursor, the capsule wall may be ruptured by an external pressure such as mechanical pressure, thereby introducing the fill material into its surroundings. Generally, the microcapsules comprise separate and discrete capsules having non-interconnecting hollow spaces. The fill material is thus enveloped within the generally continuous polymeric walls of the microcapsules, which may range from about 0.1 to about 500 microns in diameter.
For many years, carbonless copy systems of the prior art utilized a standard encapsulated carbonless dye, crystal violet lactone. This was not entirely satisfactory because photocopying machines often could not distinguish the blue color. Black dyes were subsequently developed to solve the photocopy problems; however, these dyes were quite expensive. Both of these systems suffered from the disadvantage that only one color could be formed on the copy sheet.
There has been a need in the carbonless copy field for a system that will enable the formation of multiple colors on a sheet, a given color to be formed only in a selected region of the sheet. Carbonless copy systems have been disclosed whereby only selected areas or regions of a sheet would receive a colored image. These systems are disclosed, for example, in U.S. Pat. No. 4,597,993 to Okada et al., U.S. Pat. No. 4,532,200 to Arney et al., U.S. Pat. No. Re. 30,116 to Maalouf and U.S. Pat. No. 3,364,052 to Martino. However, these patents do not disclose a carbonless copy system that enables the formation of multiple colors on the sheets, with a given color to be formed only in selected regions of the sheets.
It is an object of the present invention to provide a carbonless copy system that enables the formation of multiple colored images on a recording sheet, with each colored image capable of being formed in selected regions of the recording sheet.
It is another object of the present invention to provide a carbonless copy system that enables the formation of three different colors on a recording sheet utilizing only two different dye capsules.
It is a further object of the present invention to provide a carbonless copy system that enables the formation of n! different colors on a recording sheet utilizing only n different dye precursor materials.